The present invention is directed to a process of forming a nitroparaffin and nitroaromatic compounds by gaseous phase reaction of an organic olefinic unsaturated hydrocarbon with NO.sub.2. The present process provides a method to form pre-selected nitro compounds based on the particular olefin unsaturated hydrocarbon feed.
Processes to form nitroparaffins by gaseous phase nitration are known. U.S. Pat. Nos. 3,780,115 and 3,869,253 teach that nitration of saturated hydrocarbons higher than methane can be accomplished by contacting the hydrocarbon feed with nitrogen dioxide in the presence of oxygen, such as in the form of air. The reactant gases are preheated and then introduced into the reaction zone where the gaseous phase nitration is carried out at elevated pressure and at elevated temperature. The gaseous effluent emitted from the nitration reaction zone is rapidly quenched. The quenched mixture then enters a separator where the gaseous materials in the form of unreacted hydrocarbon, nitric oxide, carbon monoxide and carbon dioxide are removed for subsequent purification and recycling and the remaining phase liquid materials are separated by decantation and the nitroparaffins are recovered by distillation. This nitration process yields a mixture of products which require further separation and purification.
French Publication No. 78/32,118 discloses that the nitroparaffins product mixture can be made to have an increased yield of nitromethane, the most commercially desired product, by utilizing ethane as the hydrocarbon feed in the homogeneous gas phase nitration. The nitration process can be further enhanced by recycling into the hydrocarbon feed some of the nitropropane product and/or by conducting the nitration in the presence of an inert gas such as nitrogen, hydrogen or argon.
U.S. Pat. No. 4,260,838, similar to the above French reference, teaches that the gas phase nitration process of U.S. Pat. Nos. 3,780,115 and 3,869,253 can be improved by altering the feed stock to obtain suitable percentages of different nitroparaffins as suits the needs of the marketplace. This patent teaches that the feed stock be made up of a mixture containing propane preferably recycled nitroparaffin and possibly inert gas and/or another alkane. The nitrating agent can be either nitrogen dioxide or nitric acid.
Each of the conventional processes, as described in the above referenced patents, relies on the use of a saturated hydrocarbon feed which provides a nitroparaffin product mixture. These processes have the further defect of providing low yield of nitroparaffin mixture and low selectivity of the most commercially desired compound, nitromethane.
The nitration of olefins has been previously suggested in U.S. Pat. Nos. 2,402,315; 2,472,550; and 2,999,119. The early patents teach that olefins will react with N.sub.2 O.sub.4 in the presence of a liquid solvent, such as ether to give dinitrogenated addition products which, when hydrolyzed, would form nitroalkanes. Large amounts of by-products of little value were formed. In '119 one is directed to carry out the reaction at low temperatures in an aromatic solvent and to rapidly remove the product from the nitrating agent in order to enhance the yield of nitroalkane. These solution processes have not met great acceptability because they are multistep reactions, require the use of a liquid solvent from which the products must be separated and provide the desired nitroalkanes as a mixture along with large amounts of degraded products.
A method to selectively form particular nitroalkanes from easily available and processable feed is highly desired. It is particularly desired to have a process to selectively form nitromethane, a very industrially useful product.